1. Field of the Invention
The present invention relates to a motor cooling apparatus for a refrigerator and, more particularly, it relates to an apparatus for cooling the main motor in the refrigerator, the refrigerator further including an evaporator, a condenser and a compressor, and the main motor serving to actuate the compressor.
2. Related Art
A conventionally-proposed typical motor cooling apparatus for the refrigerator which includes the evaporator, condenser, compressor and main motor for actuating the compressor is disclosed in Laid-open Japanese Pat. Publication No. 110963/1983. Such conventional motor cooling apparatus as taught in the publication is constructed in such a manner that the internal space of the main motor is connected to the condenser and that a guide passage is provided to introduce or guide refrigerant liquid condensed in the condenser to the internal space of the main motor by means of a refrigerant pump to cool the motor.
The conventional motor cooling apparatus constructed according to the above-described manner has an advantage that the refrigerator can save significant energy because the motor is cooled by discharging heat produced inside the motor directly to cooling water in the condenser without using the compression power of the refrigerator.
The latent heat of vaporization of the refrigerant liquid is used to eliminate the heat produced inside the motor in the case of the abovementioned motor cooling apparatus. According to the study of the inventors of the present invention, however, it has been found that a flow amount of refrigerant liquid larger than that calculated on the assumption that all of the refrigerant supplied evaporates is needed to smoothly remove the heat inside the motor and achieve a uniform cooling effect. Particularly, the suction pipe position of the refrigerant liquid supply pump at which the suction pipe is connected to the condenser is not appropriate and when the refrigerator is operated under small load, the amount of refrigerant liquid sufficient to meet the suction capacity of the pump is not obtained to cause cavitation. As a result, the amount of refrigerant liquid which is to be supplied to the motor becomes largely insufficient, and the motor temperature rises accordingly.
In the case of this motor cooling apparatus, a part of the refrigerant liquid which has been supplied to the motor evaporates at the time of its cooling the motor and is again condensed to refrigerant liquid by the condenser. The remainder of the refrigerant liquid is left not evaporated in the motor is returned to the condenser to join the refrigerant liquid in the condenser. The refrigerant liquid thus joined is sucked into the pump through a pipe-connected opening in the bottom of the condenser to form a cycle through which it is fed to the motor. On the other hand, refrigerant gas discharged from the compressor is also condensed in the condenser and this condensed refrigerant liquid flows through a passage in the bottom of the condenser, which is connected to the evaporator, and a throttle mechanism such as the orifice into the evaporator.
As described above, both of the refrigerant liquid circulated to cool the motor and the one circulated through the refrigerating cycle are joined each other and again divided in the condenser. When the refrigerator is operated under small load, therefore, the amount of the refrigerant gas discharged from the compressor decreases and the amount of the refrigerant liquid produced when the refrigerant gas is condensed also decreases. On the other hand, the amount of the refrigerant liquid circulated through the motor cooling cycle is almost changed because it is circulated by the pump. However, the refrigerant liquid flowing out of the condenser has been joined and then divided on the bottom of the condenser, whichever cycle it may be circulated through. When the pipe connection opening or port to the pump is not appropriately located, the amount of the refrigerant liquid sucked into the pump to cool the motor is not balanced with the amount of the refrigerant liquid flowing to the evaporator, thereby allowing a part of the refrigerant liquid, which is to be sucked into the pump, to flow into the evaporator, because the refrigerator which is provided with the fixed throttle mechanism such as the orifice has no mechanism of decreasing the amount of the refrigerant liquid flowing into the evaporator.
The amount of the refrigerant liquid circulated through the motor cooling cycle is thus reduced and the effective suction pressure of the pump is lowered, to cause the cavitation. As the result, the flow amount of the refrigerant liquid is decreased remarkably and the motor temperature is raised.
In order to prevent such cavitation, it is necessary that the required forcing pressure or net positive suction head (NPSH) of the refrigerant pump is increased, or that the positional difference in vertical direction between the refrigerant liquid discharge port of the condenser and the refrigerant liquid suction port of the refrigerant pump is made substantially large. This, however, causes the condenser to be located at an elevated position and the refrigerator must be large-sized accordingly.
It would therefore be desirable to provide a motor cooling apparatus for the refrigerator capable of reducing the saturated vapor pressure of refrigerant liquid at the suction port of the refrigerant pump, which serves to feed the refrigerant liquid through the motor cooling cycle, so as to prevent the cavitation of the refrigerant pump